I think this is a good idea. Right now Fortress is very imm-centric, and dependent on the availability or interest of Padwei and Baerinika to run their cabals. A tiered system like the way you describe adds an additional layer of RP, as well as sense of accomplishment and balance. Templar is a nice middle-road name for the Maran, what about the Acolytes? Disciple, perhaps, although I think "Disciple" would likely rank higher than an "Acolyte, assuming a monastery setting.